This invention relates to fuel cells and, more particularly, relates to fuel cells that are provided with either a dual electrode anode or a dual electrode cathode. Such a dual electrode cell is operable to either produce electrical energy simultaneously from a gaseous fuel and a liquid fuel, in the case of a dual electrode anode, or to simultaneously reduce a gaseous oxidant and a liquid oxidant, in the case of a dual electrode cathode.
The use of fuel cells for the production of electric energy is generally well known. During the first hundred years after the operating principles of simple fuel cells were known, such cells were largely experimental curiosities, because only relatively low-power cells were developed. By the 1950's, however, fuel cells capable of generating several kilowatts of electrical energy were successfully built and operated. Since that time, significant advances have been made in developing fuel cells so that now many different types of cells are in common use. For example, fuel cells have successfully utilized both acidic and alkaline electrolytes, and cells have been developed that utilize either gaseous fuels such as hydrogen, or liquid fuels such as alcohol. Either oxygen or air is normally used as the oxidant in modern fuel cells, but liquid oxidants such as hydrogen peroxide have also been successfully employed.
Although extensive experimentation and development of fuel cells has taken place heretofore, the basic structural components of such cells has remained largely unchanged, at least insofar as all known prior art fuel cells utilize a single electrode anode and a single electrode cathode that are operably mounted in mutual contact with a suitable electrolyte. Current is conducted between the anode and cathode electrodes responsive to electro-oxidization of a fuel within the cell. Furthermore, such generally known fuel cell structures are designed to operate with either a gaseous or a liquid fuel being applied to their respective anode electrodes, rather than being designed to operate with both a gaseous and a liquid fuel being simultaneously applied to their anodes. Similarly, all known prior art fuel cells appear to be designed to operate with either a gaseous or a liquid oxidant being applied to their respective cathode electrodes, rather than being capable of simultaneously reducing both a gaseous and liquid oxidants at their cathodes.
Because of the inherent advantages of fuel cells, relative to alternative technologies for producing electrical energy, efforts are now being made to develop fuel cells that can operate on more complex fuels than those commonly used in earlier cells. In particular, it would be desirable to consume fossil fuels, such as coal in fuel cells. If the chemical energy of coal could be used to produce electrical energy in efficient fuel cells, rather than continuing to be used in conventional combustion processes, with their resultant production of wastes and pollutants and the requirement that associated inefficient transducers be used, it is recognized that many desirable benefits would be realized. For example, fuel cells are noiseless and operate at relatively high efficiencies without creating objectionable by-products of combustion. Moreover, the simple static elements of fuel cells are generally much less expensive to manufacture and maintain in operation than are conventional combustors and associated transducers such as those typically used in steam turbine power generating power systems.
In early development work on fuel cells that can consume coal-derived synthesis gas as a fuel, both alkaline and acidic electrolytes have been considered. In addition, the possible use of both molten carbonate and solid electrolytes has been considered. With such relatively complex synthesis gas fuels, it was anticipated that carbonate formation would foreclose the use of alkaline electrolytes, even though they are generally regarded as superior to other types of electrolytes because such alkaline cells generally have lower operating temperatures and higher performance characteristics and are likely to be less expensive to construct and operate. However, recent experiments with a number of alkaline electrolytes, such as hydroxides, sodium silicate and alkaline carbonates in fuel cells powered by coal-derived synthesis gases has established that certain alkaline electrolytes can be successfully used in such cells without incurring unacceptable levels of carbonate formation. As an evaluation criteria for those experiments, it was decided that a pH level of greater than 10.0 and a resistivity of less than 10 Ohm cm, at about 25.degree. C., should be maintained in the electrolyte along with substantial invariance with CO.sub.2. As a result of such experiments, it was determined that CO, which is a major constituent of such coal derived synthesis gas fuels, is converted to formate before it is oxidized to carbon dioxide. Further, it had been hypothesized that the performance of such fuel cells would most probably be limited by concentrations of formate at their anodes, because it is known that formate can be readily electro-oxidized. Accordingly, it was suggested that if formate could be elevated, the performance of such fuel cells could be improved dramatically. Those experimental results and hypotheses are more fully discussed in a paper authored by the present applicant entitled, "Utilization of Carbonaceous Fuels in Alkaline Fuel Cells", which was presented at the II Simposio Interuniversitario De Energia, at Santiago, Chile, during a meeting in November 1983.
It would be advantageous in controlling the operation of fuel cells designed for use with complex fuels, such as those derived from coal synthesis, to develop a fuel cell structure that can be operated to control the concentration of formate present at the anode of the cell. Furthermore, it is foreseen that for some desired future fuel cell applications it will also be desirable to have means for controlling the application of two different oxidants at the cathode of a fuel cell.